Lotus Elan

Oversteer on corners

PostPost by: john.p.clegg » Fri Feb 09, 2018 12:21 pm

My geometry says 0.3 degrees toe-in on all wheels , one of yours matches that , rear left,but the rear right is toeing out?
And the fronts have been reduced from 0.42 to 0.13 degrees ?

Maybe my theory/numbers is rubbish??

The machine is only as good as the man operating it , with the information he has...

John :wink:
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PostPost by: MarkDa » Fri Feb 09, 2018 12:27 pm

So the upshot us that LH rear is toed-in a bit much bearing in mind that angle should be about 1.5 times total mid point front toe-in but RH is well out?
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PostPost by: JonB » Fri Feb 09, 2018 12:36 pm

I'm not sure Mark, it's all a bit too confusing for me.

I need to find a way to get a bit more front caster. It's vague at speed in a straight line and can even drift a little with no steering input (tramlining?). It does feel better, but it's still not making me feel it is handling like a proper Lotus. And it is still diving into the bends, though perhaps not as much.

If only I could get someone who knew the cars to drive it and give me an opinion. Right now all I have is my own subjectivity. :(

Edit. Just had a chat with someone @ Spyder. Front caster can be adjusted, minutely, by fitting washers / shims to the top wishbone pin and ball joint bolts. Seems a bit marginal. They do sell an adjustable top wishbone but we're looking at something like ?350 for the setup, which seems a bit OTT to me.
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PostPost by: gus » Fri Feb 09, 2018 1:23 pm

What I am seeing in the numbers is a lot of things changing that are not adjustable, so either there is too much play or the machine is messed up.

I mean, how exactly is he adjusting rear camber?

You can add caster to the front, I did so and it helps in highway stability. You just add a spacer to the front of the top ball joint and then between the chassis and the rear top wishbone.

While the variance in the rear numbers could be bushings, it could also be struts or lotacones.
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PostPost by: nmauduit » Fri Feb 09, 2018 2:28 pm

JonB wrote:Here are the results from the laser alignment check.

What is a bit bothering is that values that are not adjustable (e.g. camber) have varied between the "before" and the "after", suggesting that the car was not loaded the same before and after, hence voiding the comparison.

As for the toe-in settings, I'm not sure of the optimal or preferred settings for a Plus2, but the sheet shows a significant reduction after adjustment (0.13? instead of ~0.45?)... on a 2 seater I usually stay at the top of the window (~0.25? per front wheel, 3/32" each side).

The non null thrust angle (should be 0.00?) and dissymmetry of the rear end may push you to investigate what is causing it (A-arm, chassis etc...) : it may be one of the causes of the observed instability when entering/exiting a curve (rolling=loading or unloading a rear wheel with dissymmetry and non null thrust).

JonB wrote:@nmaudit, thanks for the diagrams. I don't think anyone is suggesting I am experiencing "rear bump steer", and I do not see how it is possible with fixed suspension mounts and new bushes (there may be some bush flex but I seriously doubt it is enough to influence the steering. However you must be aware that these cars are sensitive to rear toe in angles, and as we can see, mine is out of kilter.

possibly not in this thread, but my comment was mostly discussing to the other thread cited in reference just before my reply and from which I have taken an excerpt that clearly pushes that hypothesis, which I refute.
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PostPost by: JonB » Fri Feb 09, 2018 2:45 pm

Well, it looks like I am going to be fitting A frame adjusters. I just ordered a set of turnbuckles. so at least the rear toe in can be setup properly, once I weld them into the rear wishbones. It's a bit of a pig because I am going to have to remove / refit them - not my favourite job.
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PostPost by: pauljones » Fri Feb 09, 2018 3:10 pm

JonB

Did you change the bushes?

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PostPost by: JonB » Fri Feb 09, 2018 3:20 pm

On the rear, yes.

On the front, no.

I will correct that!
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PostPost by: AussieJohn » Fri Feb 09, 2018 3:34 pm

A general "look out for" a friend who was replacing all bushes with original style found that the inner steel bush was not concentric with the outer steel bush; a possible cause of some guys alignment problems.
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PostPost by: pauljones » Fri Feb 09, 2018 4:41 pm

Jon

Can you measure the bottom A arms? I may be wrong but i was under the impression the rear was non adjustable.
Id also check the position of the mounting points from the center line, i cant help thinking its twisted. Perhaps in a former life its been hit.
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PostPost by: JonB » Fri Feb 09, 2018 4:47 pm

No evidence of damage - confirmed by the guy who did the tracking. If the frame really is out of kilter, I'm afraid I don't want to know, it's too horrible to contemplate. I will address the things I can fix myself, first.

You're correct, the rear is not adjustable, unless adjustable wishbones are fitted (these allow toe in to be set). As I am trying not to spend every penny I have on the car, I am going to modify my wishbones like this:

lotus-suspension-f42/frame-adjuster-t30315.html#p202546

I have ordered the turnbuckles and will get a local firm to machine the sleeves and do the welding. For the front suspension, I have ordered a full set of bushes from Sue Miller. I'll be dismantling everything this weekend. What joy.
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PostPost by: pauljones » Fri Feb 09, 2018 5:00 pm

So assuming chassis is correct and new bushes to prevent unwanted movement,

When the guy set it up did he ensure it was at correct ride height. I think its 5in above ground level. Its been said in other posts that if this is not followed it will not give accurate readings when laden.

And have you used origonal rubber bushes or poly, nothing other than for my own curiosity. I was thinking of poly myself, just after info on ride.
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PostPost by: tonyr27 » Fri Feb 09, 2018 7:34 pm

Are the wheels straight, as a buckled wheel will change the values if the car or wheel positions are moved.

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PostPost by: mark030358 » Fri Feb 09, 2018 8:36 pm

possibly not in this thread, but my comment was mostly discussing to the other thread cited in reference just before my reply and from which I have taken an excerpt that clearly pushes that hypothesis, which I refute


Errmmmm are you alluding to my link and the results obtained? I can 101% say that the car did not drive well until I took to the changes I listed, quoted below. Yes, it may have been the crap Dunlops, yes it may have been a wheel, but in all honesty I dont think so as the wheels and tyres I took off were in excellent condition. I honestly believe the geometry changes that were made fixed all my problems.

Never in my ownershp of my Sprint have I ever felt really comfortable driving at speed. The car was running on the origional steel wheels and Dunlop SP10's and had been previously set up as best possible.

So bit the bullet and went the whole hog. Four new Minilite 5x13, four new XAS 155x13, complete TTR rear suspension (including all drive shafts, due to QED 420 cams.. another story).

So all fitted ond off to the alignement garage.....

Front toe in 2 mm overall (interesting that the rods ran out of adjustment, I think the arms are slightly too long. Read this on another thread somewhere)
Front camber 1/4 degree negative each side

Rear toe in 3.1 mm per side
Rear camber just under 1/4 negative each side

and WoW!!!

Car is super stable, never been like this before at +100mph (allegedly) the car is rock solid and stable, no twitches, side to side movement, just fantastic. I have never had it so good before.

Over the moon .... just great.

Oh and running 19 psi front, 24 psi rear.

cheers


And nowhere does it mention rear bump steer in my post.
thanks
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PostPost by: JonB » Fri Feb 09, 2018 9:58 pm

pauljones wrote:So assuming chassis is correct and new bushes to prevent unwanted movement,

When the guy set it up did he ensure it was at correct ride height. I think its 5in above ground level. Its been said in other posts that if this is not followed it will not give accurate readings when laden.

And have you used origonal rubber bushes or poly, nothing other than for my own curiosity. I was thinking of poly myself, just after info on ride.


Laden when tested with 2 adult occupants' worth of weight.
Rubber bushes. I was told by another member that he'd used poly and they didn't last.
Only new on rear, front to be done.

Frankly, does not matter if measurements are inaccurate as it handles like a dog for a Lotus. So something is definitely wrong. (What I'm saying is, even if the measurements are out, the car is also out, so the net effect is the same - lousy handling.)
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